Theranostic nanoshells: from probe design to imaging and treatment of cancer

Abstract

Recent advances in nanoscience and biomedicine have expanded our ability to design and construct multifunctional nanoparticles that combine targeting, therapeutic, and diagnostic functions within a single nanoscale complex. The theranostic capabilities of gold nanoshells, spherical nanoparticles with silica cores and gold shells, have attracted tremendous attention over the past decade as nanoshells have emerged as a promising tool for cancer therapy and bioimaging enhancement. This Account examines the design and synthesis of nanoshell-based theranostic agents, their plasmon-derived optical properties, and their corresponding applications. We discuss the design and preparation of nanoshell complexes and their ability to enhance the photoluminescence of fluorophores while maintaining their properties as MR contrast agents. In this Account, we discuss the underlying physical principles that contribute to the photothermal response of nanoshells. We then elucidate the photophysical processes that induce nanoshells to enhance the fluorescence of weak near-infrared fluorophores. Nanoshells illuminated with resonant light are either strong optical absorbers or scatterers, properties that give rise to their unique capabilities. These physical processes have been harnessed to visualize and eliminate cancer cells. We describe the application of nanoshells as a contrast agent for optical coherence tomography of breast carcinoma cells in vivo. Our recent studies examine nanoshells as a multimodal theranostic probe, using these nanoparticles for near-infrared fluorescence and magnetic resonance imaging (MRI) and for the photothermal ablation of cancer cells. Multimodal nanoshells show theranostic potential for imaging subcutaneous breast cancer tumors in animal models and the distribution of tumors in various tissues. Nanoshells also show promise as light-triggered gene therapy vectors, adding temporal control to the spatial control characteristic of nanoparticle-based gene therapy approaches. We describe the fabrication of DNA-conjugated nanoshell complexes and compare the efficiency of light-induced and thermally-induced release of DNA. Double-stranded DNA nanoshells also provide a way to deliver small molecules into cells: we describe the delivery and light-triggered release of DAPI (4',6-diamidino-2-phenylindole), a dye molecule used to stain DNA in the nuclei of cells.

FIGURE 1

OCT images of normal tissue of mice systemically injected with (a) PBS and (b) nanoshells and tumor tissue injected with (c) PBS and (d) nanoshells. The dark nonscattering layer is 200 µm thick glass of the probe. (e) Tumor size before irradiation and 12 days post-irradiation with near-infrared laser of mice treated with nanoshells (white), PBS (gray) and untreated control (black). Reproduced with permission from ref..

FIGURE 2

(a) Illustration of nanocomplexes fabrication and conjugation to antibodies. (b) Spin–spin relaxation rate (T₂ ⁻¹) as a function of [Fe] of the nanocomplexes. r₂ is relaxivity obtained from the slope. (c) Fluorescence (FL) spectra of enhanced ICG doped within silica layer of nanocomplexes, and unenhanced control, ICG doped within silica nanospheres. Reproduced with permission from ref..

FIGURE 3

Images of SKBR3 cells (top) and control, MDAMB231 cells (bottom), incubated with nanocomplex–anti-HER2 conjugates. (a, b) MR images of nanocomplexes bound to cells suspended in agarose. (c, d) Maximum intensity projection of T₂ maps of the images corresponding to (a) and (b) respectively. Fluorescence images of (e) SKBR3 cells showing nanocomplexes binding on cell surface, (f) MDAMB231 cells showing some nonspecific binding (g, h) Photothermal ablation of cells incubated with nanocomplex–anti-HER2 and treated with NIR laser at 808 nm. Live cells are stained green with calcein and dead cells are stained red with PI. Reproduced with permission from ref..

FIGURE 4

Nanocomplexes delivery in vivo observed with near-infrared fluorescence imaging of mice with (a) control, MDAMB231 xenografts (top) and BT474AZ xenografts (bottom) at 0.3–72 h post-injection of nanocomplexes. T₂-weighted MRI images of (b) MDAMB231 xenografts (top) and BT474AZ xenografts (bottom) pre-injection 0 h, and 4–72 h post-injection of nanocomplexes. Tumor is marked with red circle. (c) Near-infrared fluorescence images of mice tissues harvested from BT474AZ (left) and MDAMB231 (right) 72 h post-injection of nanocomplexes. (d) Fluorescence intensity analysis of mice organs of BT474AZ (red) and MDAMB231 (black). (e) Gold distribution (from ICP-MS) in mice tissue. Reproduced with permission from ref..

FIGURE 5

(a) Schematic of light-controlled release of ssDNA from nanoshells when illuminated with resonant near-infrared light. Thiolated sense sequences (green) are bound to nanoshell surface and antisense sequences (red) are released. (b) Comparison of light-induced (green) versus thermal (red) dehybridization of dsDNA sequences of different lengths tethered to nanoshells. (c) Thermal and (d) light-induced release of ssDNA from dsDNA-coated nanoshells in solution. Melting curves for 20 base dsDNA attached to nanoshell surface are shown. Insets show first derivatives of the melting curves, depicting melting temperatures of each process. Reproduced with permission from ref..

FIGURE 6

Flow cytometry histograms of DAPI Fluorescence versus number of isolated nuclei from H1299 cells incubated with (a) nanoshell-dsDNA-DAPI and (b) DAPI (control). Control (gray), treated cells without laser irradiation (blue) and treated cells with laser irradiation (red). Bar graphs display the mean DAPI fluorescence intensity±SEM before and after laser irradiation. (c) Epifluorescence images of H1299 cells incubated with nanoshell-dsDNA-DAPI (left) before and (right) after laser treatment. The cell membrane is marked by Alexa-Fluor488 (green). Reproduced with permission from ref..